1. Field of the Invention
The present invention relates to an automatic speed control device for a vehicle. More particularly, it relates to an automatic speed control device which is capable of preventing a vehicle from approaching the preceding vehicle incautiously.
2. Description of the Related Art
There is an earlier automatic speed control device which includes a distance measuring sensor for detecting a distance and an angle between the vehicle concerned and the preceding vehicle. Note, the distance between the driver's vehicle and the preceding vehicle will be referred as "distance between the vehicles", hereinafter. In the automatic speed control device, when detecting the preceding vehicle during traveling at a speed established by a driver, the driver's vehicle is automatically decelerated for a distance (or a time) predetermined corresponding to respective traveling velocities of the driver's vehicle and the preceding vehicle and thereafter, the driver's vehicle is traveled while keeping the distance between the vehicles. When the preceding vehicle changes its traffic lane and disappears from a traffic lane of the driver's vehicle, then it is automatically accelerated up to the speed established in advance.
In the conventional automatic speed control device, however, when the distance measuring sensor loses track of the preceding vehicle under the influence of, for example, curves, slopes, weather or the like, there is a possibility of causing a problem that the driver's vehicle is automatically accelerated in spite of existence of the preceding vehicle, so that the distance between the vehicles is reduced incautiously.